Synchronizing an engine is the operation that consists in determining the angular position of an engine. This determination is essential in order then to be able to control the engine and to inject fuel at the appropriate moment in the engine cycle, for example.
To this end, an engine, such as an internal combustion engine, includes a crankshaft sensor and at least one camshaft sensor.
A crankshaft sensor comprises a crankshaft toothed wheel, joined to the crankshaft so as to rotate therewith and comprising a large number of regular teeth and a revolution marker. The crankshaft sensor also comprises a crankshaft detector facing said crankshaft toothed wheel and able to detect a presence/absence of material and thus to detect a tooth or a slot.
The crankshaft toothed wheel is angularly divided equally into a large number of regular teeth, thus making it possible to accurately ascertain the angular position of the crankshaft. The crankshaft toothed wheel also comprises a revolution marker, enabling an absolute referencing of a given angular position once per revolution. Said revolution marker is generally associated with a position of the engine, such as, conventionally, the top dead center of the first cylinder.
However, for a four-stroke engine, a crankshaft performs exactly two revolutions per engine cycle. Therefore, ascertaining the angular position of the revolution marker is not enough to indicate the angular position of the engine, since said position is known with an uncertainty of one revolution out of two.
In order to specify which revolution out of two the engine is on, use may be made of a camshaft sensor.
A camshaft sensor comprises a camshaft toothed wheel, joined to a camshaft so as to rotate therewith and comprising a small number of teeth that are advantageously irregular. The camshaft sensor also comprises a camshaft detector facing said camshaft toothed wheel and able to detect a presence/absence of material and thus to detect a tooth or a slot.
The small number of teeth of the camshaft toothed wheel does not make it possible to accurately ascertain the angular position of the camshaft and therefore of the engine. However, a camshaft performs exactly one revolution per engine cycle. Therefore, this feature makes it possible to remove doubt with regard to which crankshaft revolution out of two is involved and thus, alongside the information obtained from the crankshaft sensor, to completely determine the angular position of the engine.
Said removal of doubt/determination of the crankshaft revolution out of two is achieved by identifying the teeth and slots of the camshaft toothed wheel on the basis of their respective length, resulting from a known camshaft toothed wheel profile.
Said removal of doubt/determination is typically achieved as quickly as possible, in fast mode, as soon as a match with said profile is confirmed.
However, such an operating mode may be deceived, in a detrimental manner, if the engine changes its direction of rotation and rotates in the reverse direction. If an engine is deemed to be synchronized, while it is rotating in the reverse direction, an injection of fuel may be ordered, which may lead to adverse effects for the engine.